1. Field of the Invention
The present invention relates to an image forming apparatus in which sheets are discharged into any one of a plurality of sheet stacking means.
2. Description of the Related Art
There has been proposed a discharging option for a printer in which movable discharging bins have only one sensor for detecting the amount of paper stacked in each discharging bin and the detection is performed by moving each discharging bin. In addition, a method of controlling a printer connected to the discharging option has been proposed. In this control method, a print instruction is received from a host computer and command analyzing is performed. The determination whether to start is based on previously-obtained discharging-bin information rather than on the present state of the discharging bin.
The above-described conventional examples have the following problems:
In the printer, only while actual feeding and discharging is performed can the condition of the discharging bin in use be detected. If the discharging bin is already full when the print instruction is received, several sheets are still printed because the detection of the stacked-paper amount is performed during actual discharging. Accordingly, several sheets are discharged into the fully-stacked discharging bin before notification of the full stack is issued. In other words, if the discharging bin is changed by a discharging-bin selecting instruction transmitted as part of print data from the host computer, the stacked-paper amount in the selected discharging bin cannot be detected until the previous sheets are discharged by performing the next printing because a discharging bin into which the previous discharging was performed had been operational (in a condition capable of detecting the stacked-paper amount). Accordingly, the processing must be performed based on the previous information. In the case of a discharging system with one single sensor that can detect only the stacked-paper amount in the operational discharging bin, detection is impossible when a user removes paper or puts paper in a discharging bin other than the operational discharging bin. The system cannot operate based on accurate information because only the stacked-paper amount in the operational discharging bin can be detected.
As described above, only after discharging is started can an accurate stacked-paper amount be detected. Thus, a discharging bin that is already full may be used as the selected discharging bin. Thus, sheets are discharged into the fully-stacked discharging bin, and paper jamming occurs in the discharging system, which often causes malfunctioning.
In the case where paper in the fully-stacked discharging bin, which is not operational, is removed by the user, a problem occurs in that the discharging system has determined that the bin is fully stacked, and prohibits the discharging bin from being used despite the fact that paper can be practically stacked in the discharging bin.
In the case where the discharging system has two modes: an automatic discharging mode for discharging into an empty discharging bin, and a fixed discharging mode for discharging into one fixed discharging bin. the modes may be mixed when being used by a plurality of users in a network environment. If in the automatic discharging mode, a user performs a job that needs discharging a large amount of paper, the paper may be discharged into a plurality of discharging bins. By way of example. in the case where a user A performs fixed outputting to a second discharging bin, and another user B uses the automatic discharging mode to perform a large-amount of outputting to a first discharging bin as a starting point, the output of user B is discharged into the second discharging bin after the first discharging bin is full. Thus, the output of user B is stacked on the output of user A. The output of user A is mixed in the output of user B. Therefore, user B, who does not know that the output of user A has been discharged into the second discharging bin may mistakenly remove the output of user A.